package com.wc.alorithm_luogu._二分.P1163_银行贷款;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2024/3/17 20:28
 * @description https://www.luogu.com.cn/problem/P1163
 */

public class Main {
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int W, w, m;


    // 公式 W = w / (1 + p) + w / (1 + p)^2 + w / (1 + p)^3  + ... + w / (1 + p) ^ m
    public static void main(String[] args) {
        W = sc.nextInt();
        w = sc.nextInt();
        m = sc.nextInt();
        double l = 0, r = 3;
        while (r - l > 1e-6) {
            double mid = (l + r) / 2;
            if (check(mid)) l = mid;
            else r = mid;
        }
        out.printf("%.1f", l * 100);
        out.flush();
    }

    static boolean check(double mid) {
        double s = 0;
        double v = 1;
        for (int i = 1; i <= m; i++) {
            v *= (1 + mid);
            s += w / v;
        }
        return s >= W;
    }
}

class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}